common api - null equivalence (#15926)

closes https://github.com/twentyhq/core-team-issues/issues/1629

To do before requesting review : 
- filter update

Migration to come in an other PR


Strat : 
1/  Null transformation

- [x] Transform NULL equivalent value to NULL in field validation in
common api - pre-query - with feature flag
- [ ] Same logic in ORM (Not done, complex to handle feature flag here)
- [x] Transform NULL value to equivalent in data formatting in ORM -
post-query

2/ Migration (in other PR) for fieldMetadata not nullable with default
defaultValue (empty string, ...)

- [ ] Remove NOT NULL db constraint
- [ ] Update record value to NULL
- [ ] Update field metadata : isNullable:true
- [ ] Update uniqueIndex whereClause (also for standard uniqueIndex) 
- [ ] Activate feature flag

3/ Update metadata creation

- [x] No more default default value
- [x] Update standard field nullability
- [x] Remove index default whereClause for standard field

4/ Update filter

- [x] When filtering on NULL or empty string, be sure all records are
returned (the one with NULL + the one with "")

5/ Test

- [ ] Strat. to do

packages/twenty-server/src/engine/workspace-manager/workspace-migration-builder/factories/utils/__tests__/workspace-migration-index.factory.util.spec.ts

@@ -46,7 +46,7 @@ describe('WorkspaceMigrationIndexFactory', () => {
     expect(firstMigration.indexes[0].columns).toEqual(['simpleField']);
     expect(firstMigration.indexes[0].type).toBe('BTREE');
     expect(firstMigration.indexes[0].isUnique).toBe(true);
-    expect(firstMigration.indexes[0].where).toBe('"simpleField" != \'\'');
+    expect(firstMigration.indexes[0].where).toBeNull();
   });
 
   it('should create index migrations for relation fields', async () => {

packages/twenty-server/src/engine/workspace-manager/workspace-migration-builder/factories/utils/workspace-migration-index.factory.utils.ts

@@ -1,7 +1,7 @@
 import {
-  FieldMetadataType,
   type CompositeType,
   compositeTypeDefinitions,
+  FieldMetadataType,
 } from 'twenty-shared/types';
 import { isDefined } from 'twenty-shared/utils';
 
@@ -92,17 +92,13 @@ export const createIndexMigration = async (
         .flat()
         .filter(isDefined);
 
-      const defaultWhereClause = indexMetadata.isUnique
-        ? `${columns.map((column) => `"${column}"`).join(" != '' AND ")} != ''`
-        : null;
-
       return {
         name: indexMetadata.name,
         action: WorkspaceMigrationIndexActionType.CREATE,
         isUnique: indexMetadata.isUnique,
         columns,
         type: indexMetadata.indexType,
-        where: indexMetadata.indexWhereClause ?? defaultWhereClause,
+        where: indexMetadata.indexWhereClause,
       };
     });